1. Field of the Invention
The invention relates to a high-power radiator, in particular for ultraviolet light, having a discharge space which is filled with a fill-gas emitting radiation under discharging conditions and whose walls are formed by an outer and an inner tubular dielectric which are provided in each case on the surfaces averted from the discharge space with an inner and an outer electrode, and having an alternating current source for feeding the discharge connected to these electrodes.
The invention refers in this regard to a prior art such as emerges for example, from EP-A 0,254,111, corresponding to U.S. Pat. No. 4,837,484 the U.S. Pat. No. 5,013,959.
2. Discussion of Background
The industrial use of photochemical processes depends strongly on the UV sources suitable for availability. The classic UV radiators deliver low to medium UV intensities at a few discrete wavelengths such as, for example, the low-pressure mercury lamps at 185 nm and, in particular, at 254 nm. Truly high UV outputs are obtained only from high-pressure lamps (Xe, Hg), which then, however, distribute their radiation over a larger range of wavelengths. The new excimer lasers have provided a few new wavelengths for photochemical basic experiments, and for reasons of cost are presently suitable for an industrial process probably only in exceptional cases.
In the EP Patent Application named at the beginning, or else in the printed conference publication "Neue UV- und VUV Excimerstrahler" ("New UV and VUV Excimer Radiators") by U. Kogelschatz and B. Eliasson, distributed at the 10th Lecture Conference of the Society of German Chemists, Specialist Group for Photochemistry, in Wurzburg (FRG) 18-20th November 1987, there is a description of a new excimer radiator. This new type of radiator is based on the principle that excimer radiation can also be generated in silent electrical discharges, a type of discharge which is used on a large industrial scale in ozone generation. In the current filaments of this discharge, which are present only briefly (&lt;1 microsecond), rare gas molecules are excited by electron collision and further react to form excited molecule complexes (excimers). These excimers live only a few 100 nanoseconds, and release their binding energy upon decay in the form of UV radiation.
The structure of such an excimer radiator largely corresponds to that of a classic ozone generator, with the essential difference that at least one of electrodes and/or dielectric layers limiting the discharge space is transparent to the radiation generated.
The high-power radiators mentioned are typified by high efficiency and an economic structure, and permit the creation of sizeable large-area radiators, with the restriction that large-format flat radiators rather require a high technical outlay. In the known cylindrical radiators, by contrast, a considerable proportion of the radiation is not utilized due to the shading effect of the inner electrode. In order, now, to increase the yield in cylindrical radiators, in the case of the conventional radiators the inner dielectric tubes are very small by comparison with the outer dielectric tubes. A preferred direction of the emission is achieved through an eccentric arrangement of the inner dielectrics, having a small diameter by comparison with the diameter of the outer dielectrics, and of the outer electrodes only on the surface adjoining the inner dielectric, and the simultaneous formation of the outer electrode as a reflector.